Chemistry

Growing Sugar Crystals with String and Making Rock Candy



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Growing sugar crystals can be a fun project to do with younger kids on a rainy day, or as a science experiment for a school project. There are several ways to do this, including the string method.

Here are some materials that you can gather before starting:

Glass or plastic cup (this should be able to handle very hot water)
Pencil or popsicle stick
Heavy string or thin twine
Sugar - about a five pound bag
A spoon
Food coloring
Paper towel

*Note: the first step will be working with very hot water. For safety reasons only an adult should perform the first steps. PLEASE REMEMBER TO KEEP SMALL CHILDREN AND PETS AWAY FROM THE HOT WATER.

To start, get a microwave safe container, like a Pyrex measuring cup. Fill it with water to about the one cup mark. Place this cup of water in the microwave and set it for five minutes at high heat. You will want the water very hot to effectively dissolve the sugar into it.

While the water is heating, take the string or twine and tie one end around the pencil or popsicle stick (the string holder). Now get your glass or plastic cup that you will use to contain your crystals in (the cup) and place the pencil or popsicle stick across the top of the cup and center it so the string falls down  into the center of the glass. Note the length of the string and cut it so that the end is about an inch above the bottom. Remove the string holder and string off the top of the cup.

If the water is starting to boil, *carefully* (remember only an adult should do this step) remove it from the microwave and place the hot water and the container it is in on the countertop or on a table and make sure that it is in no danger of being spilled. Don't place a spoon or other metal object in the hot water as this can sometimes make the water "erupt".

Now, this is the important part. Using your spoon, carefully add some sugar into the water (start with four teaspoons) and begin stirring the hot water. If the water is hot enough, the sugar will disappear completely and the water will remain clear. Keep adding two teaspoons of sugar to the water as soon as the water turns clear from the last sugar that was added and keep stirring in between. Continue to do this until the water either stays cloudy or undissolved sugar crystals are collecting at the bottom.

The importance of this step is that the water is getting saturated with sugar. The more sugar that you can get dissolved into the water, the bigger your crystals will grow. If you do not get enough sugar into the water, the crystal may not form properly.

If you think that you have enough sugar dissolved, you may add some food coloring to the water if you desire. If you chose a dark color, remember that it will be harder to see your crystal while it is forming, so go easy on the amount of coloring you add.

Being mindful of the hot sugar water, carefully pour the water into your experiment cup and get it about one quarter to the rim of the top. If you have extra water left over, don't throw it away: there is a back up plan that you may want to use (explained later), so pour that into another container and put that off to the side.

Take a paper towel and get it wet, then take a small amount of sugar and sprinkle it on the wet paper towel, about the size of a dime. Take your string holder and wet the string, then begin to rub it around in the spot of sugar, getting some sugar crystals to stick to the string. You don't need a lot, and they will help attract the sugar in the water to grow on them.

Let the water cool for thirty minutes and then slowly take your sugar coated string and place it into the cup and rest the string holder across the top of the cup, allowing the string to hang in the center of the sugar water solution. Carefully place this project somewhere that won't get too cold or too hot and can get to room temp slowly.

Now depending how much sugar is in the water, the rate at which the water cools and whether the seed crystals on the string encourage crystal growth, you should begin to see crystals appear on the string in a few days. Once they do they will continue to grow until there isn't enough sugar in the water to grow further.

If after 4 days you have not seen any significant growth, you may try the backup plan. The old water that you didn't use should have evaporated and left many large crystals behind. Find a piece big enough to tie to the end of your string and place that in the sugar water solution. That big piece is a seed that should do the trick of attracting crystals to grow on it.

As with any project, you may not achieve spectacular results on the first try, but experiment! Try using a large seed crystal first, add more sugar and write down the changes that you note.

Remember to always think safety first and have fun. Soon you will have many different colored crystals to show your friends and they will be begging you to show them how.


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